This invention relates to a lead frame and lead frame processing techniques for leaded semiconductor chip carriers. More particularly, the invention relates to a lead frame design and method that enables a complete and thorough testing of an assembled product in a totally non-destructive manner prior to encapsulation.
In the equipment used to produce semiconductor packages, the chips are mounted on a die pad, and connections are made from the contact areas of the die pad to similar areas in the package or the chips in the package. The external connections of the package take the form of leads which attach to the printed circuit board (PCB). The use of a surface mount technique allows the package to be small in size which in turn conserves space on the PCB.
Present manufacturing processes typically handle lead frame assemblies in strip form wherein linked lead frames each have at least one chip position. The linked lead frames are wound on reels to provide a continuous strip on which various automated steps or manufacturing processes may be performed to provide an assembled leaded semiconductor package. Such packages are either of the hermetic type or the non-hermetic type (plastic packaging) used primarily in commercial applications. For example, U.S. Pat. No. 4,214,364 provides for the hermetic and non-hermetic packaging of passive and active electrical and electronic devices, and is particularly suitable for semiconductor devices, using a common lead frame in strip form.
A major drawback of current products and packaging techniques is the inability of testing, an assembled, packages prior to encapsulation. After encapsulation it is not economically practical to open up a package to rework a chip or connection therein. In the case of molded packages, undoing the encapsulation is simply not practical. Therefore, the production yield of packaged semiconductor circuits is lowered due to the inability to rework defective assemblies. In packages containing a number of chips, the opportunity for mistakes increases with the increased number of chips and operations performed thereon. Accordingly, foregoing the opportunity to rework a chip or package is a disadvantage in terms of both relative yield itself and the absolute cost of the investment associated with the more complex chip assemblies.
One significant application of complex chip assemblies is in the case of display packages wherein a large number of devices are used in array fashion for display matrices. In general, and particularly in the latter situation, it would be highly advantageous and economically beneficial to be able to test the assembled package while still in the lead frame strips so that defective assemblies may be reworked prior to encapsulation. Such testing also should be done in a manner such that damage to the package and tiny leads of highly ductile material is reduced or eliminated.